Re: [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification

[Anthony Liguori <anthony@codemonkey.ws>]

On 10/11/2010 10:46 AM, Stefan Hajnoczi wrote:
> On Mon, Oct 11, 2010 at 05:39:01PM +0200, Avi Kivity wrote:
>    
>>   On 10/11/2010 05:30 PM, Stefan Hajnoczi wrote:
>>      
>>>>   It was discussed before, but I don't think we came to a conclusion. Are
>>>>   there any circumstances under which you don't want to set the
>>>>   QED_CF_BACKING_FORMAT flag?
>>>>          
>>> I suggest the following:
>>>
>>> QED_CF_BACKING_FORMAT_RAW = 0x1
>>>
>>> When set, the backing file is a raw image and should not be probed for
>>> its file format.  The default (unset) means that the backing image file
>>> format may be probed.
>>>
>>> Now the backing_fmt_{offset,size} are no longer necessary.
>>>        
>> Should it not be an incompatible option?  If the backing disk starts
>> with a format magic, it will be probed by an older qemu,
>> incorrectly.
>>      
> Agreed, it should be a non-compat feature bit.
>    

If it's just raw or not raw, then I agree it should be non-compat.

I think we just need a feature bit then that indicates that the backing 
file is non-probeable which certainly simplifies the implementation.

QED_F_BACKING_FORMAT_NOPROBE maybe?

Regards,

Anthony Liguori

> Stefan
>
>